1. Field of the Invention
The present invention relates to a chip packaging process. More particularly, the present invention relates to a heat sink and a method of bonding the heat sink to form a chip package.
2. Description of the Related Art
In semiconductor production, the manufacturing of integrated circuits (IC) can be divided into three different stages, namely, a wafer fabrication stage, an integrated circuit fabrication stage and an IC packaging stage. Each die is produced after conducting a series of operations including, for example, wafer fabrication, circuit design, mask production and wafer sawing. After dicing up a wafer, contacts on the die are electrically connected to external points for intercommunicating with external devices. Thereafter, a molding material is used to enclose the die and produce a package so that the die is protected from moisture, heat and electrical interference while providing a means for connecting the die with an external circuit.
As the level of integration of integrated circuit increases, a variety of packaging methods for enclosing the chip have been developed. Because the so-called flip chip technology is able to reduce chip package area and shorten overall transmission path for signals, it has been widely adopted in the production of chip packages including chip scale packages (CSP), direct chip attach (DCA) packages and multi-chip module (MCM) packages.
To increase the dissipation of heat from a chip, a heat sink is normally attached to the backside of the chip using thermal conductive glue after the chip is electrically connected to the substrate via bumps. Furthermore, to increase the overall area and area of attachment of the heat sink and to position the heat sink more accurately, an additional stiffener ring is often attached to the substrate surrounding the chip. In other words, the stiffener ring is able to increase the heat-dissipating area of the heat sink and therefore its cooling capacity.
Conventionally, the heat sink is attached to the backside of the chip and the stiffener ring via a spot gluing process. In the spot gluing process, glue is applied to the backside of the chip and the stiffener ring before attaching the heat sink. Thereafter, a curing operation is performed to lock the heat sink and the backside of the chip tightly together. However, in the attachment process, the glue is applied to the backside of the chip and the stiffener ring separately. Since a longer time is required to complete the operation, overall yield can hardly improve.